Painful Channelopathies Study

Inclusion Criteria: * Patients who are ≥16 years of age who have a set of symptoms that resemble those seen on Paroxysmal Extreme Pain Disorder, Familial Episodic Pain Syndrome or Erythromelalgia. * Patients already with the diagnosis of Paroxysmal Extreme Pain Disorder or Familial Episodic Pain Syndrome or Erythromelalgia. * Patients with reduced pain sensibility. * First degree relatives of patients who meet diagnostic criteria for Paroxysmal Extreme Pain Disorder, Familial Episodic Pain Syndrome, Erythromelalgia or inability to experience pain. * Patients who do not fulfill any of the exclusion criteria. Exclusion Criteria: * Pregnant subjects. * Subjects with insufficient command of English to obtain consent from or to complete the study questionnaires. * Subjects with insufficient mental capacity to obtain consent from or to complete the study questionnaires. * Subjects with concurrent severe psychological or psychiatric disorders, specially those patients with severe claustrophobia. * Patients with moderate to severe pain arising as a consequence of other disorders causing pain but that are not associated with those mentioned before as channelopathies. * Patients with central nervous system diseased that may complicate the somatosensory testing. * The skin biopsy procedure, will not be conducted on those patients with contraindications to do so i.e. anticoagulation therapy, skin infections, etc; that might result in adverse outcomes (if the subject decides to decline the skin biopsy, the inclusion on the study will not be affected). * The functional magnetic resonance imaging (fMRI) component will not be performed in subjects that had medical interventions with any device likely to be damaged or moved from its place, at any moment during the fMRI scanning procedure (including cerebral coils or clips, heart pacemakers or defibrillators, heart valve prosthesis, medicine infusion pumps, inner ear implants, neural stimulators, brain shunts, joint replacements/ large metal implants, stents in the heart or arteries, some implants, or some intra-uterine contraceptive devices. * Those patients that in the concept of the research team unsuitable for participation in the study. * For those undergoing microneurography presence of edema (swelling) or any skin condition at the ankle level that may interfere with the microneurography procedure. * Patients with a history of skin allergy or sensitivity will not undergo testing of axon reflex or conditioning challeng…